Recently, to improve efficiency of a safety system of a vehicle, a method for measuring weight of an occupant, e.g., a crew member or a passenger, of the vehicle using a seat weight measuring apparatus has been under development for controlling motion of the safety system. The safety system mentioned above denotes a seat belt, an airbag or the like. For example, Japanese Patent Unexamined Publication H11-1153 discloses weight measuring apparatuses which are positioned at four corners of seat rails and measure seat weight to determine the weight of an occupant.
However, even if the conventional weight measuring apparatus itself has high accuracy, when a load is applied, friction tends to occur in a vertical motion because of a positional deviation or a surface slope at a fixing section. As a result, detecting accuracy is conspicuously reduced because of a transmission loss, which is caused by the friction, of the load.